1. Field of the Invention(s)
The present invention(s) generally relate to power distribution grid network optimization strategies. More particularly, the invention(s) relate to systems and methods for switch-controlled VAR sources coupled to a power distribution grid.
2. Description of Related Art
The conventional approach to power distribution grid voltage control is based on techniques developed about 70 years ago. In recent years, highly complex and expensive systems have been required to implement improved effective voltage control and conservation voltage reduction (CVR) based demand reduction. Under present requirements, alternating current (AC) line voltage for connected users needs to fall within a narrow band specified by ANSI C84.1 under all conditions of loading and substation voltage. Typically, utilities operate in a narrow band of 116-124 volts, even though level ‘A’ service allows for a range of 114-126 volts. The difficulty in adhering to a tight regulation band arises from normal fluctuations in incoming line voltage at the substation, as well as load changes along the feeder. These changes cause the line voltage to vary, with utilities required to maintain voltage for consumers within specified bounds.
The prior art volt-ampere reactive regulation devices (VAR devices) for voltage control may be split into several categories including: 1) prior art VAR devices with slow responding capacitors and electro-mechanical switches; ii) prior art VAR devices with medium response capacitors and thyristor switched capacitors; and iii) prior art VAR devices with power converter based VAR control using Static VAR sources or static synchronous condensers (STATCOMs).
It should be noted that capacitors in the prior art VAR devices are mainly used for power factor control when used by customers and for voltage control when used by utilities. For power factor control, the downstream line current must be measured. Capacitors and/or inductors may be switched on or off based on the line current to realize a desired overall power factor (e.g., typically at a value of unity). In the second case of voltage control used by utilities, capacitors are controlled based on: 1) local voltage measurements; 2) other parameters such as temperature; 3) line reactive current; and/or 4) dispatches communicatively received from a control center. The control center may dispatch decisions regarding capacitor control based on information received from multiple points in the network.
Most capacitors of prior art VAR devices are switched using electromechanical switches. The electromechanical switches are limited in switching speed and by life of the switches. Many electromechanical switches are limited to 3-4 switches per day. A response time of approximately fifteen minutes is often required to enable voltage control with prior art VAR devices. During this time, the following steps may be performed: 1) sensing voltages locally; 2) communicating the sensed voltages to a centralized control center; 3) power and/or voltage modeling of the system at the centralized control center; 4) determining to take action based on the model and perceived potential improvements; and 5) dispatching one or more commands from the centralized control center to the prior art VAR device to switch the capacitor. More advanced Volt-VAR Optimization or VVO systems are moving to such centralized implementations so they can try to optimize the profile of voltage along an entire distribution feeder and reduce infighting between prior art VAR devices.